The present invention relates to methods and systems for measuring the water level of a body of water, whether free flowing water such as a river or stream or stationary such as a lake, reservoir or holding tank, and, more particularly, to an improved water level measuring method and system which does not involve mounting of the measurement equipment over the water surface, i.e., which enables water level measurements to be made from the edge of the water, e.g., from an embankment, platform or bridge structure adjacent to the water.
Both mechanical and electromechanical devices are used to measure what is referred to as xe2x80x9cstagexe2x80x9d or water level with respect to a datum point. This is generally done from a bridge platform or structure in or over the water. Such water level measuring devices require that the sensor be in contact with water surface and in the majority of instances, require a specially built housing or enclosure, referred to as a stilling-well installation, to dampen or filter the turbulence of water in order to obtain a correct reading. Such stilling-well installations generally employ a long, typically two-foot diameter corrugated pipe attached vertically to an adjacent platform, and extending all of the way into a water column. All water level measurement instruments currently used by the United States Geological Survey (USGS) use the contact methods in determining water level and water flow, and, in this regard, there are nearly 7,000 sites throughout the United States which contain equipment or instruments for measuring water level.
With some devices, it is difficult to obtain a measurement of water level because of the lack of a platform or other structure for mounting the measuring equipment or instrument. Further, because the placement of such structures in parks and wildlife refuges detracts from the natural beauty of the environment, the structures are often located at sites which are out of the way and difficult to get to, and substantial time and expense is incurred in transporting personnel to visit, and make measurements at, these largely inaccessible sites. Moreover, there are many areas for which water level information is needed but cannot be obtained because of the cost and manpower necessary to prepare a site for installation of equipment. Further, because at least with USGS installations, a majority of the stage measuring instruments are mounted on bridge platforms, the installation of the instruments and extraction of the data can be hazardous.
Some prior art commercial systems use measuring or sensing beams and require that the sensing or measuring beam (which may be a radar beam or laser beam) be mounted such that the beam projects directly vertically downward to the water surface. Further, the characteristics of the measuring beam itself (e.g., whether in pulsed mode or continuous mode of operation) are employed in making the measurement, and this can often complicate the associated electronic circuitry required. In such systems, beam characteristics such as time-of-flight or change in phase are used in determining the water level, in contrast to the present invention which, as explained below, uses simple geometry in calculating the water level.
In accordance with the invention, a method and system are provided for the determination of the water level of both free flowing bodies of water (e.g., rivers or streams) and stationary bodies of water (e.g., lakes, reservoirs or holding tanks), which overcome or substantially eliminate the above-discussed problems associated with prior art methods and devices.
Among other important advantages thereof, the invention does not require the system apparatus be positioned vertically above the water surfaces, i.e., the apparatus need not be mounted on a structure (bridge or platform) which is located over or across the water but instead can be sited and operated at the edge of the body of water. Further, the invention can be used in measuring water levels in canyons, from bluffs and in highly inaccessible areas wherein a conventional water level measurement device would normally be positioned directly vertical with respect to the water surface. Further, as indicated below, the invention makes water level measurements based on simple geometry, i.e., uses no electronic or electromechanical or mechanical contact of a sensor with the water surface, and thus eliminates the problems associated with contact systems, such as damage to the sensor caused by floating or submerged objects in free flowing water. In addition, installation of the invention at new sites, which is done periodically by the USGS, can be carried out with substantial cost savings, because, inter alia, there is no need for stilling wells.
In accordance with one aspect of the invention, a system is provided for determining the level of a body of water, whether free flowing or stationary, the system comprising: at least one positionable reflective element located at an area adjacent to, but spaced from, the body of water, for directing a laser beam at an angle to true vertical onto the surface of the body of water such that at least a portion of the directed beam is reflected from the surface; a signal detector for producing an output in response to receiving a laser beam; a receiver, located at a determined distance from the reflective element on the opposite side of the body of water from the reflective element and in a common horizontal plane with the reflective element, for receiving the reflected laser beam and redirecting the beam to said signal detector; and a controller for controlling positioning of the positionable reflective element at a determined angle to true vertical at which the reflected beam is received by the receiver, for receiving said output from the signal detector, and for calculating, based on said determined angle and the determined distance between the reflective element and the receiver, the distance from the common horizontal plane to the water surface so as to determine the water level.
Preferably, the at least one reflective element comprises first and second mirrors for reflecting the laser beam along two orthogonal axes. Advantageously, the first and second mirrors comprise vertical and horizontal positioning mirrors. The system preferably further comprises positioning motors controlled by the controller for controlling the positioning of the mirrors. Advantageously, the positioning motors comprise stepping motor or voltage controlled motors.
In a preferred embodiment, the system further comprises input means for inputting data to the controller. The input means advantageously comprises a keyboard. In addition, a display unit is preferably provided for displaying the determined water level and other data.
The receiver advantageously comprises receiver optics for receiving the reflected beam and at least one corner prism for redirecting the beam to the signal detector.
In accordance with a further aspect of the invention, a method is provided for determining the level of a body of water, whether free flowing or stationary, the method comprising: directing a laser beam at a variable angle to true vertical from a positionable reflective element, located at an area adjacent to but spaced from the body of water, onto the surface of the body of water such that at least a portion of the beam is reflected from the surface; receiving the portion of the beam reflected from the surface with a receiver located on the opposite side of the body of water from, and in substantially the same horizontal plane as, the reflective element, and redirecting the reflected beam so received to a signal detector for producing an output signaling reception of the redirected reflected beam; determining the angle to true vertical at which the portion of the reflected beam is received by said receiver responsive to receiving said output from the signal detector; and using (i) the angle to true vertical so determined, and (ii) the distance between the reflective element and the receiver, to calculate the distance from said horizontal plane to the water surface so as to determine the water level.
Preferably, the laser beam is dithered and a plurality of angle data points are taken in determining the angle to true vertical.
In a preferred embodiment, the reflective element comprises horizontal and vertical positionable mirrors and the method further comprises controlling the positions of the mirrors in determining the angle to true vertical. Preferably, the angle of the mirrors is initially set by a microcontroller at a predetermined angle (e.g., 0xc2x0) with respect to true vertical and the angle of the mirrors is thereafter increased by the microcontroller until the reflected beam is received by the receiver. Advantageously, the signal detector signals the microcontroller when the reflected beam is received by the receiver and the microcontroller then determines the current angles of the mirrors. In one advantageous implementation, the signal detector is located in close proximity to the microcontroller and is electrically connected to the microcontroller.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.